Such copolymers are usually prepared in suspension in chlorofluorocarbon solvents, in an aqueous suspension or in an aqueous emulsion.
The polymerization in suspension in chlorofluorocarbon solvents does not permit fast reaction speeds to be achieved even if the process is to be carried out under low pressures and at low temperatures.
Regarding polymerization in aqueous suspension, considerably large amounts of tert.-butanol, which is the main constituent of the reaction medium, have to be used in the processes disclosed in U.S. Pat. Nos. 2,479,367 and 3,870,689. Furthermore, with these techniques, discharging the reaction products from the reactor is not easy, in that a slurry is obtained, which is difficult to be handled.
In U.S. Pat. No. 3,859,262, use is proposed of particular salts of manganese as polymerization initiators. These salts increase the reaction speed. However, although use of organic solvents is avoided, the disclosed process does not permit reaction speeds greater than 60 grams of tetrafluoroethylene/ethylene copolymer per liter per hour. Still in this patent, a technique of polymerization in aqueous emulsion is disclosed. This disclosure does not permit reaction speeds of 85 grams of copolymer per liter per hour to be exceeded. One should finally observe that use of chain transfer agents for regulating molecular weight of the obtained polymers causes a further decrease in reaction speed.
In U.S. Pat. No. 4,426,501, a process is taught for carrying out the synthesis of tetrafluoroethylene-ethylene copolymers in aqueous emulsion, which permits greater reaction speeds to be obtained. According to such a process, the reaction should be carried out at 95.degree. C. under a pressure of 4.1 MPa. Under such conditions, to prevent explosion risks, a gaseous mixture fed to the reactor is diluted with chloropentafluoroethane.
The above disadvantages are avoided by the present invention over the above references which are hereby incorporated by reference.